Heretofore, in an automated assembly line for automobiles, an assembly process has been carried out in which clamping is carried out by a clamp apparatus under a condition in which pre-formed frames are positioned in an overlaid manner and the frames are welded together.
As one such clamp apparatus, as disclosed in Japanese Patent No. 4950123, a pair of left and right clamp arms are provided, the clamp arms being disposed for rotation respectively through pins, and ends of the clamp arms are supported pivotally via a base to which a drive unit is connected, whereby distal ends of the clamp arms are operated to open and close. Thus, a workpiece such as a frame or the like is gripped from the left and the right by the distal ends of the pair of clamp arms.